Voltage regulator has been applied in various electronic products to serve as power supply for providing stable supply voltages. FIG. 1 schematically shows a typical voltage regulator 100, which comprises a pair of high side transistor 102 and low side transistor 104 coupled between input voltage Vin and ground GND to be alternatively switched by PWM controller 105 to produce an output current Iout flowing through an inductor L to charge an output capacitor C1 to produce an output voltage Vout. In the PWM controller 105, current sense circuit 116 senses the output current Iout to generate a current sense signal Isen supplied for a reference voltage generator 110 to generate a reference voltage Vref, error amplifier 108 generates an error signal EA from the difference between the output voltage Vout and reference voltage Vref for a comparator 112 to compare with ramp signal Vramp provided by ramp generator 114 to produce pulse width modulation signal PWM for driver 106 to switch the transistor 102 and 104. FIG. 2 shows a functional block diagram of the reference voltage generator 110, in which digital to analog converter (DAC) 118 converts digital signal VID to analog voltage V1, the current sense signal Isen inputs to droop unit 122 to generate droop voltage Vdroop, offset unit 120 provides offset voltage Voffset, and those voltages V1, Vdroop and Voffset are combined together by summing circuit 124 to generate the reference voltage Vref.
When load on the voltage regulator 100 changes from light to heavy, mass heat will be generated from various sources, such as switching loss, conduction loss, charging/discharging, and inductor loss, among which the heat caused by conduction loss, charging/discharging, and inductor loss is dependent on hardware, and the total heat could be reduced by reducing switching loss.
Therefore, it is desired a PWM controller for a voltage regulator to reduce the switching loss of the voltage regulator.